1. Field of the Invention
The present invention relates to packet data services provided in communication systems, and more particularly, to a method and apparatus for transmitting and receiving service packet data and associated control information to and from a mobile terminal by utilizing disparate physical channels for receiving the packet data and the associated control information.
2. Discussion of the Related Art
The universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from the global system for mobile communications system, which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access technologies.
A conventional UMTS network structure 1 is illustrated in FIG. 1. One mobile terminal 2, or user equipment (UE), is connected to a core network 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains, and manages a radio access bearer for communications between the UE 2 and core network 4 to meet end-to-end quality-of-service requirements.
The UTRAN 6 includes a plurality of radio network subsystems 8, each of which comprises one radio network controller (RNC) 10 for a plurality of base stations 12, or “Node Bs.” The RNC 10 connected to a given base station 12 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 2 operating in one cell. The controlling RNC 10 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 12 may receive an uplink signal from a UE 2 and may transmit downlink signals to the UE. Each Node B 12 serves as an access point enabling a UE 2 to connect to the UTRAN 6, while an RNC 10 serves as an access point for connecting the corresponding Node Bs to the core network 4.
Among the radio network subsystems 8 of the UTRAN 6, the serving RNC 10 is the RNC managing dedicated radio resources for the provision of services to a specific UE 2 and is the access point to the core network 4 for data transfer of the specific UE. All other RNCs 10 connected to the UE 2 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 4 via the UTRAN 6. The drift RNCs 10 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 2 and UTRAN 6 is realized through a radio interface protocol established in accordance with 3GPP radio access network specifications describing a physical layer (L1), a data link layer (L2), and a network layer (L3). A control plane is provided for carrying control information for the maintenance and management of the interface and a user plane is provided for carrying data traffic such as voice signals and Internet protocol packet transmissions. The conventional architecture of the radio interface protocol is illustrated in FIG. 2.
The physical (PHY) layer provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. The MAC layer includes a MAC-b entity, a MAC-d entity, and a MAC-c/sh entity.
The MAC-b entity manages the broadcast channel as a transport channel responsible for the broadcasting of system information. The MAC-c/sh entity manages common transport channels shared with other UEs 2 within the cell, for example the forward access channel and downlink shared channel, such that one MAC-c/sh entity exists for each cell and is located at the serving RNC 10. Therefore, each UE 2 has one MAC-c/sh entity. The MAC-d entity manages a dedicated transport channel with respect to a specific UE 2 such that the MAC-d entity is located at the serving RNC 10 and each UE also has one MAC-d entity.
A radio link control (RLC) layer supports the transmission of reliable data and is responsible for the segmentation and concatenation of RLC service data units delivered from a higher layer. The size of the RLC service data unit is adjusted for the processing capacity in the RLC layer and a header is appended to form an RLC protocol data unit for delivery to the MAC layer.
The formed units of service data and protocol data delivered from the higher layer are stored in an RLC buffer of the RLC layer. The RLC services are used by service-specific protocol layers on the user plane, namely a broadcast/multicast control (BMC) protocol and a packet data convergence protocol (PDCP), and are used by a radio resource control (RRC) layer for signaling transport on the control plane.
The BMC layer schedules a cell broadcast message delivered from the core network and enables the cell broadcast message to be broadcast to the corresponding UEs 2 in the appropriate cell. Header information, such as a message identification, a serial number, and a coding scheme, is added to the cell broadcast message to generate a broadcast/multicast control message for delivery to the RLC layer.
The RLC layer appends RLC header information and transmits the thus-formed message to the MAC layer via a common traffic channel as a logical channel. The MAC layer maps the common traffic channel to a forward access channel as a transport channel. The transport channel is mapped to a secondary common control physical channel as a physical channel.
The PDCP layer serves to transfer data efficiently over a radio interface having a relatively small bandwidth. The PDCP layer uses a network protocol such as IPv4 or IPv6 and a header compression technique for eliminating unnecessary control information utilized in a wire network. The PDCP layer enhances transmission efficiency since only the information essential to the header is included in the transfer.
The RRC layer handles the control plane signaling of the network layer (L3) between the UEs 2 and the UTRAN 6 and controls the transport and physical channels for the establishment, reconfiguration, and release of radio bearers. A radio bearer is a service provided by a lower layer, such as the RLC layer or MAC layer, for data transfer between the UE 2 and UTRAN 6.
Establishment of a radio bearer determines the regulating characteristics of the protocol layer and channel needed to provide a specific service, thereby establishing the parameters and operational methods of the service. When a connection is established to allow transmission between an RRC layer of a specific UE 2 and an RRC layer of the UTRAN 6, the UE is said to be in the RRC-connected state. Without such connection, the UE 2 is in an idle state.
In addition to the above-described entities of the MAC layer, a MAC-m entity is provided to support the user-plane and control-plane transmissions for point-to-multipoint services, for example a multimedia broadcast/multicast service (MBMS), and to handle the scheduling of MBMS-related transport channels. An MBMS is a streaming or background service provided to a plurality of UEs 2 using a downlink-dedicated MBMS radio bearer that utilizes both point-to-multipoint and point-to-point radio bearer services.
As the name implies, an MBMS may be carried out in a broadcast mode or a multicast mode. The broadcast mode is for transmitting multimedia data to all UEs 2 within a broadcast area, for example the domain where the broadcast service is available. The multicast mode is for transmitting multimedia data to a specific UE 2 group within a multicast area, for example the domain where the multicast service is available.
When a UMTS network 1 provides a specific MBMS using the multicast mode, UEs 2 to be provided with the service must first complete a subscription procedure establishing a relationship between a service provider and each UE individually. Thereafter, the subscriber UE 2 receives a service announcement from the core network 4 confirming subscription and including, for example, a list of services to be provided.
The subscriber UE 2 must “join,” or participate in, a multicast group of UEs receiving the specific MBMS, thereby notifying the network 4 of its intention to receive the service. Terminating participation in the service is called “leaving.” The subscription, joining, and leaving operations may be performed by each UE 2 at any time prior to, during, or after the data transfer.
While a specific MBMS is in progress, one or more service sessions may sequentially take place, and the core network 4 informs the RNC 10 of a session start when data is generated by an MBMS data source and informs the RNC of a session stop when the data transfer is aborted. Therefore, a data transfer for the specific MBMS may be performed for the time between the session start and the session stop, during which time only participating UEs 2 can receive the data.
To achieve successful data transfer, the UTRAN 6 receives a notification of the session start from the core network 4 and transmits an MBMS notification to the participating UEs 2 in a prescribed cell to indicate that the data transfer is imminent. The UTRAN 6 uses the MBMS notification to count the number of participating UEs 2 within the prescribed cell.
Through the counting process, it is determined whether the radio bearer providing the specific MBMS is one for a point-to-multipoint transmission or a point-to-point transmission. To select the MBMS radio bearer for a specific service, the UTRAN 6 sets a threshold corresponding to the UE 2 count, whereby a low UE count establishes a point-to-point MBMS radio bearer and a high UE count establishes a point-to-multipoint MBMS radio bearer.
The radio bearer determination is based on whether the participating UEs 2 need to be in the RRC-connected state. When a point-to-point radio bearer is established, all of the participating UEs 2 are in the RRC-connected state. When a point-to-multipoint radio bearer is established, it is unnecessary for all of the participating UEs 2 to be in the RRC-connected mode since the point-to-multipoint radio bearer enables reception by UEs in the idle state.
Referring now to FIG. 3, the conventional architecture of an MBMS-supported MAC layer is illustrated. A MAC-c/sh/m entity supports two logical channels, specifically the MBMS control channel (MCCH) and the MBMS traffic channel (MTCH).
One MCCH channel exists in each cell and one MTCH channel exists for each specific MBMS within a specific cell. Both logical channels are mapped to a transport channel, such as the forward access channel (FACH), and to a physical channel, such as the secondary control physical channel (SCCPCH).
An example of conventional logical channel mapping is illustrated in FIG. 4A. FIG. 4A illustrates a mapping structure of the logical channels MTCH and MCCH, whereby the logical channels are respectively mapped to different physical channels, for example to first and second physical channels SCCPCH 1 and SCCPCH 2.
FIG. 4B shows an example of conventional transmission of MBMS data for a specific MBMS and the control information associated with the service. As illustrated in FIG. 4B, logical channel MCCH is a point-to-multipoint downlink channel for transferring MBMS control plane information and logical channel MTCH is a point-to-multipoint downlink channel for transferring MBMS user plane information.
Since the logical channels MCCH and MTCH are each mapped to a unique physical channel, an MBMS-supportable UE 2 must simultaneously receive two physical channels in order to receive the service. There is simultaneous transmission of user information and control information, for example the MBMS data over the MTCH channel and the MBMS control information over the MCCH channel.
However, a UE 2 may be unable to support the simultaneous reception of two different physical channels. Therefore, the UE 2 may be unable to receive either the MBMS data or the MBMS control information.
Even assuming a UE 2 that supports simultaneous reception of two different physical channels, the UE may actually need to receive three or more physical channels simultaneously if the reception of a service in addition to the MBMS is desired. Therefore, the requirement for simultaneous reception of the two logical channels, MCCH and MTCH, hinders enhanced UE 2 operation.
Therefore, there is a need for a method and apparatus for enabling a mobile terminal not having the capability to simultaneously receive two different physical channels to receive a service that is transmitted using at least two logical channels. The present invention addresses these and other needs.